1. Field of the Invention
The present invention relates generally to a rongeur surgical instrument, and more particularly to an improved rongeur surgical instrument having a trigger mechanism providing a variable mechanical advantage for operation of the cutting element in the instrument, and also having an improved shaft design which both maintains cutting edge alignment with the footplate anvil surface and provides a mechanism for preventing cut portions of body material from aggregating near the distal end of the shaft and interfering with the cutting operation.
In surgical procedures, having a properly designed instrument is crucial to allow the surgeon to optimize treatment for the patient. One such instrument used in certain procedures is a surgical instrument called a rongeur, which is a heavy-duty cutting forceps for removing small pieces of bone, cartilage, or other tough body tissue from small spaces in the human body. Rongeurs are typically used in conjunction with procedures on vertebrae of the back, as well as in procedures on the knee.
A rongeur typically includes an extended two-piece shaft supported at the proximal end by a grip which may be pistol-shaped. One of the shaft members is fixed with respect to the grip, and has a transversely mounted footplate mounted at its distal end. The other shaft member is moveable in reciprocating axial movement adjacent to the first shaft member, with the reciprocating movement being caused by squeezing of a triggering mechanism pivotally mounted with respect to the grip.
The distal end of the second shaft member is generally axially aligned with the footplate mounted on the first shaft member. The distal end of the second shaft member contains a cutting member positioned for engagement with the footplate when the second shaft member is in its most distal position. As the trigger is squeezed, the distal end of the second shaft member moves against the footplate, which acts as an anvil surface. By placing bone or tissue to be cut between the cutting member and the footplate and then squeezing the trigger, small segments of the bone or tissue may be removed with a high degree of precision.
It will at once be appreciated by those skilled in the art that since the areas in which a rongeur is used are small, the distal end of the shaft must by necessity be quite small. As such, the footplate must also be quite small and relatively thin. This brings conflicting design requirements into view. Since a surgeon using a rongeur will typically be cutting hard materials such as bone or cartilage, the forces present at the footplate and cutting member are quite large. The small sizes of the footplate and the cutting member, dictated by the small areas in which the rongeur must operate, make them susceptible to bending or misalignment.
The related patent application which was incorporated by reference above solves this problem by seeking to limit transverse movement of the distal end of the second shaft member with respect to the distal end of the first shaft member, and also by limiting the amount of force the surgeon may apply to the cutting member against the footplate. The limit on transverse movement of the second shaft member is provided by having inwardly extending tabs on side portions of the distal end of the second shaft member engaging slots in the side of the distal end of the first shaft member. This of course helps considerably, but with the application of sufficient force the side portions may actually be bent outwardly sufficiently to allow the tabs to escape engagement with the slots, allowing misalignment of the cutting member with respect to the footplate.
Thus, it is an objective of the present invention that it provide a more positive mechanism for maintaining the relative alignment of the cutting member and the footplate in a rongeur surgical instrument. It is also a further objective that the mechanism for maintaining alignment of the cutting member and the footplate not interfere in any way with the cutting operation of the surgical instrument, or with the surgeon's vision of the cutting operation. It is a related objective that this desirable design ambition be achieved without increasing the size of the members in any way, thereby maintaining a small distal shaft configuration.
Another area for improvement is in the actuation of the trigger member to move the cutting member into engagement with the footplate. Every rongeur design in the past has used a linear trigger member and constant linear actuation of the cutting member. Thus, movement of the trigger member in a first amount will always cause movement of the cutting member in a second amount. It would be advantageous for movement of the trigger member to cause a greater degree of movement of the cutting member prior to engagement of bone or tissue, when less precision of movement, as well as less of a mechanical advantage, is required. Upon engagement of the bone or tissue between the cutting member and the footplate, it would then be advantageous for movement of the trigger member to cause a lesser degree of movement of the cutting member, when greater precision of movement, as well as more of a mechanical advantage, is required.
It is accordingly a primary objective of the present invention to provide a variable degree of mechanical advantage to the trigger-actuated operation of the movement of the cutting member toward the footplate. During initial actuation of the trigger member to initiate movement of the cutting member toward the footplate prior to engagement of bone or tissue, it is thus an objective to provide a lesser degree of mechanical advantage, together with a greater degree of movement of the cutting member. In contrast, during actuation of the trigger subsequent to engagement of bone or tissue between the cutting member and the footplate, it is an objective to provide a greater degree of mechanical advantage, together with a lesser degree of movement of the cutting member.
Another problem encountered in operation of a rongeur is the aggregation of bone or tissue chips previously cut in the cutting area, where they can interfere with the engagement of additional portions of bone or tissue to be cut. The cutting member at the distal end of the second shaft member may have a tunnel therein, as disclosed in the related patent application which was incorporated by reference above. This tunnel is designed to allow bone and tissue chips to be carried proximally away from the footplate and out of the path of the cutting member. However, what typically happens is that the reciprocating movement of the second shaft member with respect to the first shaft member causes bone and tissue chips to move distally out of the tunnel (during movement of the second shaft member in a proximal direction), and to inhibit future cutting operations of the rongeur by their presence between the cutting member and the footplate.
It is thus also a primary objective of the present invention that it provide a mechanism for inhibiting movement of bone or tissue chips, once cut, distally out of the tunnel in the cutting member. This mechanism should thus provide a restriction on the movement of the bone or tissue chips, but without restricting in any way the cutting operation of the surgical instrument. Thus, the mechanism for inhibiting movement of bone or tissue chips to the location of the cutting operation should enhance the ease of the cutting operation by not requiring the surgeon to pause to remove bone or tissue chips from the cutting members.
A further problem of the rongeur surgical instruments presently available is that they have a grip which is designed to fit an "average" size hand. Since the size of surgeons' hands may vary substantially, it may be seen that the fit of the grip of such known rongeurs represents a compromise, fitting only an "average" size hand well. For those surgeons having hands which are either larger or smaller than average, the fit of the grip of such rongeurs will be something less than ideal.
It is thus yet another objective of the rongeur surgical instrument of the present invention that it provide a grip which is adjustable to provide a custom fit to a wide variety of hand sizes. The variable fit of the grip should be capable of being modified to provide a comfortable accommodation for any hand size through a simple adjustment which may be quickly accomplished. It is an additional objective of the rongeur surgical instrument of the present invention that it be of solid construction, to be both durable and long-lasting in operation. Finally, it is also an objective that all of the aforesaid advantages and objectives of the present invention be achieved without incurring any substantial relative disadvantage.